Folks,
I am proposing to extend the xhtml package slightly to better support
attribute munging.
Currently you would use (!) to add a bunch of attributes to an element,
thus:
b1 = button noHtml ! [name "go", value "go"]
The problem, as pointed out by mistuke[1] is that there is no way to safely
add attributes as this could result in an attribute being bound ambiguously
and illegally [2] thus:
b2 = b1 ! [value "oops"]
Apparently this can lead Haddock to generate illegal (X)HTML [1].
My proposed solution is to add a new CHANGEATTRS class with the overloaded
function:
changeAttrs :: CHANGEATTRS a => a -> ([HtmlAttr] ->
[HtmlAttr]) -> a
and to export a function for analysing the (abstract) HtmlAttr type:
htmlAttrPair :: HtmlAttr -> (String, String)
CHANGEATTRS/changeAttrs/htmlAttrPair works just like ADDATTRS/(!) except
that the attributes can be analysed and transformed.
extend_name :: Html -> Html
extend_name h = h `changeAttrs` map f
where
f a = case htmlAttrPair a of
("name",nm) -> name $ "foo_" ++ nm
_ -> a
Finally, I have an embarrassing confession to make -- I forgot that I should
be getting the changes reviewed here -- even for such a modest widening of
the API -- and have already put out
3000.2.1 with these additions onto Hackage!
Comments and feedback welcome though,
Chris
[1] https://github.com/haskell/xhtml/issues/2
[2] http://www.w3.org/WAI/GL/WCAG20-TECHS/H94.html
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